Medical imaging apparatus such as CT Scanners use a plurality of processors to obtain the desired tomograph. The scientists who design such equipment are continuously seeking ways and means for reducing the quantity of computations required to obtain the tomograph, while maintaining high picture quality of good resolution with minimal artifacts. Such designers are continuously compromising between quantity of computations required and the quality of the tomograph.
Examples of such comprises are found, for example, in U.S. Pat. Nos. Re. 30,947 and 4,075,492, which are also concerned with CT Scanners using fan or divergent beams. Rather than proceeding with the significantly greater number of computations, required with divergent beams, the patents offer the compromise solution of reordering the divergent rays of the fan beam to parallel rays. However, the spacing between rays obtained by the reordering process in laterally unequal. The unequal spacing results in artifacts (diminution of picture quality).
To remove the artifacts, the Re. 30947 patent teaches interpolation of all the shadowgram data to "reposition" the parallel rays to laterally equal spacing. The patented system performs significantly fewer computations than would be required if the back-projection reconstruction used the original divergent beams. However, the process still requires a great number of computations.